1. Field of the Invention
The present invention generally relates to flame retarded polyurethane foams, and particularly concerns flame retarded, low density polyurethane foams having improved color characteristics.
2. The Prior Art
When low density polyurethane foams are treated with flame retardants to reduce their flammability, certain physical properties of the foams are detrimentally affected. One of the frequent problems is scorching of the center of the foam buns which results in unacceptable color of the foam. This discoloration is reduced to an acceptable level pursuant to the present invention by incorporating certain amine antioxidants into the foam.
It is known in the prior art to utilize amine antioxidants to stabilize polyurethane foams against degradation caused by light oxidation. See, for example, U.S. Pat. Nos. 3,351,608 and 3,497,457. However, the prior art has not heretofore recognized the utility of amine antioxidants to prevent cure-induced scorch of flame retardant polyurethane foams. In extreme cases, smoldering combustion can occur in the foam buns. Such problems cause loss and destruction of saleable material.
The present invention is directed to foams that do not become unacceptably scorched in the absence of a flame retardant. When the flame retardant is added to the foam formulation, however, unacceptable scorch results. It is a theory of the present invention that this scorching is the result of halogen catalyzed autooxidation of the polyether moieties present in the foam formulation. The amine antioxidants of the present invention react with the halogen atoms thereby terminating the autooxidation chain reaction.